SW4220602_Design Calculations (Riprap)_20220921

DESIGN CALCULATIONS
for
NORDFAB SYSTEMS —BUILDING EXPANSION
THOMASVILLE, NORTH CAROLINA
DMP Project 210238
Contents:
Pipe Outlet Protection Calculations
September 2022
Prepared by:
DAMS • MARTIN • POWELL
ENGINEERS & SURVEYORS
T: 336-886-4821 • F: 336-886-4458 • License: F-0245
6415 Old Plank Road, High Point, NC 27265 • www.dmp-inc.com
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Design of RipRap Outlet Protection
Project: Nordfab
Proj. No: 210238.00
Client:
Nordfab/Fourth Elm
Date:
20-Jun-22
Revised:
21-Sep-22
Site Location (City/Town) Thomasville
Culvert Id. Pipe 1 (Ditchline D-1)
Total Drainage Area (acres) 1.6
dm
—p
Davis • Martin • Powell
6415 Old Plank Road
High Point, NC 27265
p. 336.886.4821
Step 1- Determine the tailwater depth from channel characteristics below
the pipe outlet for the design capacity of the pipe. If the tailwater depth is
less than half the outlet pipe diameter, it is classified minimum tailwater
condition. If it is greater than half the pipe diameter, it is classified maximum
condition. Pipes that outlet onto wide flat areas with no defined channel are
assumed to have a minimum tailwater condition unless reliable flood stage
Outlet pipe diameter, Do (in.) 15
Tailwater depth (in.) 12
Minimum/Maximum tailwater? Max TW (Fig. 8.06b)
Discharge (cfs) 6.2 Outlet Velocity < allowable;
Velocity (ft./s) 4.5 dissipator not required
Step 2 - Based on the tailwater conditions determined in Step 1, enter
Figure 8.06a or Figure 8.06b and determine d50 riprap size and minimum
apron length (Q. the d50 size is the median stone size in a well -graded rip -
rap apron.
Step 3 - Determine apron width at the pipe outlet, the apron shape and the
Riprap d50, (ft.)
Minimum apron length, La (ft.)
Apron width at pipe outlet (ft.)
Apron shape
Apron width at outlet end (ft.)
Minimum TW
Figure 8.06a
3.75
Trapezoidal
1.25
Maximum TW
Figure 8.06b
3.75
1.25
Page 2 of 19

Design of RipRap Outlet Protection
dm
—p
Project:
Nordfab
Davis • Martin • Powell
Proj. No:
210238.00
6415 Old Plank Road
Client:
Nordfab/Fourth Elm
High Point, NC 27265
Date:
20-Jun-22
p. 336.886.4821
Revised:
21-Sep-22
Site Location (City/Town) Thomasville
Culvert Id. Pipe 1 (Ditchline D-1)
Total Drainage Area (acres) 1.6
Step 4 - Determine the maximum stone diameter:
dmax=l.5xd50
Minimum TW Maximum TW
Max Stone Diameter, dmax (ft.) 0 0
Step 5 - Determine the apron thickness:
Apron thickness = 1.5 xdmax
Minimum TW Maximum TW
Apron Thickness(ft.) 0 0
Step 6 - Fit the riprap apron to the site by making it level for the minimum length, L,
from Figure 8.06a or Figure 8.06b. Extend the apron farther downstream and along
channel banks until stability is assured. Keep the apron as straight as possible and
align it with the flow of the receiving stream. Make any necessary alignment bends
near the pipe outlet so that the entrance into the receiving stream is straight.
Some locations may require lining of the entire channel section to assure stability.
It may be necessary to increase the size of riprap where protection of the channle side
slopes is necessary (Appendix 8.05). Where overfalls exist at pipe outlets or flows are
Page 3 of 19

Design of RipRap Outlet Protection
Project: Nordfab
Proj. No: 210238.00
Client:
Nordfab/Fourth Elm
Date:
20-Jun-22
Revised:
21-Sep-22
Site Location (City/Town) Thomasville
Culvert Id. Pipe 2 (Ditchline D-2)
Total Drainage Area (acres) 2.1
dm
—p
Davis • Martin • Powell
6415 Old Plank Road
High Point, NC 27265
p. 336.886.4821
Step 1- Determine the tailwater depth from channel characteristics below
the pipe outlet for the design capacity of the pipe. If the tailwater depth is
less than half the outlet pipe diameter, it is classified minimum tailwater
condition. If it is greater than half the pipe diameter, it is classified maximum
condition. Pipes that outlet onto wide flat areas with no defined channel are
assumed to have a minimum tailwater condition unless reliable flood stage
Outlet pipe diameter, Do (in.) 18
Tailwater depth (in.) 14
Minimum/Maximum tailwater? Max TW (Fig. 8.06b)
Discharge (cfs) 8.2
Velocity (ft./s) 5.3
Step 2 - Based on the tailwater conditions determined in Step 1, enter
Figure 8.06a or Figure 8.06b and determine d50 riprap size and minimum
apron length (Q. the d50 size is the median stone size in a well -graded rip -
rap apron.
Step 3 - Determine apron width at the pipe outlet, the apron shape and the
Riprap d50, (ft.)
Minimum apron length, La (ft.)
Apron width at pipe outlet (ft.)
Apron shape
Apron width at outlet end (ft.)
Minimum TW
Figure 8.06a
0.5
10
4.5
Trapezoidal
11.5
Maximum TW
Figure 8.06b
4.5
1.5
Page 4 of 19

Design of RipRap Outlet Protection
Project: Nordfab
Proj. No: 210238.00
Client:
Nordfab/Fourth Elm
Date:
20-Jun-22
Revised:
21-Sep-22
Site Location (City/Town) Thomasville
Culvert Id. Pipe 2 (Ditchline D-2)
Total Drainage Area (acres) 2.1
Step 4 - Determine the maximum stone diameter:
dmax = 1.5 x d50
Minimum TW
Max Stone Diameter, dmax (ft.) 0.75
Step 5 - Determine the apron thickness:
Apron thickness = 1.5 xdmax
Apron Thickness(ft.)
dm
—p
Davis • Martin • Powell
6415 Old Plank Road
High Point, NC 27265
p. 336.886.4821
Maximum TW
0
Minimum TW Maximum TW
1.125 0
Step 6 - Fit the riprap apron to the site by making it level for the minimum length, L,
from Figure 8.06a or Figure 8.06b. Extend the apron farther downstream and along
channel banks until stability is assured. Keep the apron as straight as possible and
align it with the flow of the receiving stream. Make any necessary alignment bends
near the pipe outlet so that the entrance into the receiving stream is straight.
Some locations may require lining of the entire channel section to assure stability.
It may be necessary to increase the size of riprap where protection of the channle side
slopes is necessary (Appendix 8.05). Where overfalls exist at pipe outlets or flows are
Page 5 of 19

Design of RipRap Outlet Protection
Project: Nordfab
Proj. No: 210238.00
Client:
Nordfab/Fourth Elm
Date:
20-Jun-22
Revised:
21-Sep-22
Site Location (City/Town) Thomasville
Culvert Id. Pipe 3 (Ditchline D-3)
Total Drainage Area (acres) 0.5
dm
—p
Davis • Martin • Powell
6415 Old Plank Road
High Point, NC 27265
p. 336.886.4821
Step 1- Determine the tailwater depth from channel characteristics below
the pipe outlet for the design capacity of the pipe. If the tailwater depth is
less than half the outlet pipe diameter, it is classified minimum tailwater
condition. If it is greater than half the pipe diameter, it is classified maximum
condition. Pipes that outlet onto wide flat areas with no defined channel are
assumed to have a minimum tailwater condition unless reliable flood stage
Outlet pipe diameter, Do (in.) 15
Tailwater depth (in.) 6
Minimum/Maximum tailwater? Min TW (Fig. 8.06a)
Discharge (cfs) 0.75 Outlet Velocity < allowable;
Velocity (ft./s) 4.7 dissipator not required
Step 2 - Based on the tailwater conditions determined in Step 1, enter
Figure 8.06a or Figure 8.06b and determine d50 riprap size and minimum
apron length (Q. the d50 size is the median stone size in a well -graded rip -
rap apron.
Step 3 - Determine apron width at the pipe outlet, the apron shape and the
Riprap d50, (ft.)
Minimum apron length, La (ft.)
Apron width at pipe outlet (ft.)
Apron shape
Apron width at outlet end (ft.)
Minimum TW
Figure 8.06a
3.75
Trapezoidal
1.25
Maximum TW
Figure 8.06b
3.75
1.25
Page 6 of 19

Design of RipRap Outlet Protection
dm
—p
Project:
Nordfab
Davis • Martin • Powell
Proj. No:
210238.00
6415 Old Plank Road
Client:
Nordfab/Fourth Elm
High Point, NC 27265
Date:
20-Jun-22
p. 336.886.4821
Revised:
21-Sep-22
Site Location (City/Town) Thomasville
Culvert Id. Pipe 3 (Ditchline D-3)
Total Drainage Area (acres) 0.5
Step 4 - Determine the maximum stone diameter:
dmax=l.5xd50
Minimum TW Maximum TW
Max Stone Diameter, dmax (ft.) 0 0
Step 5 - Determine the apron thickness:
Apron thickness = 1.5 xdmax
Minimum TW Maximum TW
Apron Thickness(ft.) 0 0
Step 6 - Fit the riprap apron to the site by making it level for the minimum length, L,
from Figure 8.06a or Figure 8.06b. Extend the apron farther downstream and along
channel banks until stability is assured. Keep the apron as straight as possible and
align it with the flow of the receiving stream. Make any necessary alignment bends
near the pipe outlet so that the entrance into the receiving stream is straight.
Some locations may require lining of the entire channel section to assure stability.
It may be necessary to increase the size of riprap where protection of the channle side
slopes is necessary (Appendix 8.05). Where overfalls exist at pipe outlets or flows are
Page 7 of 19

Design of RipRap Outlet Protection
Project: Nordfab
Proj. No: 210238.00
Client:
Nordfab/Fourth Elm
Date:
20-Jun-22
Revised:
21-Sep-22
Site Location (City/Town) Thomasville
Culvert Id. Pipe 4 (Ditchline D-4)
Total Drainage Area (acres) 0.7
dm
—p
Davis • Martin • Powell
6415 Old Plank Road
High Point, NC 27265
p. 336.886.4821
Step 1- Determine the tailwater depth from channel characteristics below
the pipe outlet for the design capacity of the pipe. If the tailwater depth is
less than half the outlet pipe diameter, it is classified minimum tailwater
condition. If it is greater than half the pipe diameter, it is classified maximum
condition. Pipes that outlet onto wide flat areas with no defined channel are
assumed to have a minimum tailwater condition unless reliable flood stage
Outlet pipe diameter, Do (in.) 15
Tailwater depth (in.) 6
Minimum/Maximum tailwater? Min TW (Fig. 8.06a)
Discharge (cfs) 2.27
Velocity (ft./s) 7.75
Step 2 - Based on the tailwater conditions determined in Step 1, enter
Figure 8.06a or Figure 8.06b and determine d50 riprap size and minimum
apron length (Q. the d50 size is the median stone size in a well -graded rip -
rap apron.
Step 3 - Determine apron width at the pipe outlet, the apron shape and the
Riprap d50, (ft.)
Minimum apron length, La (ft.)
Apron width at pipe outlet (ft.)
Apron shape
Apron width at outlet end (ft.)
Minimum TW
Figure 8.06a
0.5
6
3.75
Trapezoidal
7.25
Maximum TW
Figure 8.06b
3.75
1.25
Page 8 of 19

Design of RipRap Outlet Protection
Project: Nordfab
Proj. No: 210238.00
Client:
Nordfab/Fourth Elm
Date:
20-Jun-22
Revised:
21-Sep-22
Site Location (City/Town) Thomasville
Culvert Id. Pipe 4 (Ditchline D-4)
Total Drainage Area (acres) 0.7
Step 4 - Determine the maximum stone diameter:
dmax = 1.5 x d50
Minimum TW
Max Stone Diameter, dmax (ft.) 0.75
Step 5 - Determine the apron thickness:
Apron thickness = 1.5 xdmax
Apron Thickness(ft.)
dm
—p
Davis • Martin • Powell
6415 Old Plank Road
High Point, NC 27265
p. 336.886.4821
Maximum TW
0
Minimum TW Maximum TW
1.125 0
Step 6 - Fit the riprap apron to the site by making it level for the minimum length, L,
from Figure 8.06a or Figure 8.06b. Extend the apron farther downstream and along
channel banks until stability is assured. Keep the apron as straight as possible and
align it with the flow of the receiving stream. Make any necessary alignment bends
near the pipe outlet so that the entrance into the receiving stream is straight.
Some locations may require lining of the entire channel section to assure stability.
It may be necessary to increase the size of riprap where protection of the channle side
slopes is necessary (Appendix 8.05). Where overfalls exist at pipe outlets or flows are
Page 9 of 19

Design of RipRap Outlet Protection
Project: Nordfab
Proj. No: 210238.00
Client:
Nordfab/Fourth Elm
Date:
20-Jun-22
Revised:
21-Sep-22
Site Location (City/Town)
Culvert Id.
Total Drainage Area (acres)
Thomasville
Slope Drain
4.97
dm
—p
Davis • Martin • Powell
6415 Old Plank Road
High Point, NC 27265
p. 336.886.4821
Step 1- Determine the tailwater depth from channel characteristics below
the pipe outlet for the design capacity of the pipe. If the tailwater depth is
less than half the outlet pipe diameter, it is classified minimum tailwater
condition. If it is greater than half the pipe diameter, it is classified maximum
condition. Pipes that outlet onto wide flat areas with no defined channel are
assumed to have a minimum tailwater condition unless reliable flood stage
Outlet pipe diameter, Do (in.) 24
Tailwater depth (in.) 6
Minimum/Maximum tailwater? Min TW (Fig. 8.06a)
Discharge (cfs) 17.5
Velocity (ft./s) 15.7
Step 2 - Based on the tailwater conditions determined in Step 1, enter
Figure 8.06a or Figure 8.06b and determine d50 riprap size and minimum
apron length (Q. the d50 size is the median stone size in a well -graded rip -
rap apron.
Step 3 - Determine apron width at the pipe outlet, the apron shape and the
Riprap d50, (ft.)
Minimum apron length, La (ft.)
Apron width at pipe outlet (ft.)
Apron shape
Apron width at outlet end (ft.)
Minimum TW
Figure 8.06a
0.5
10
6
Trapezoidal
12
Maximum TW
Figure 8.06b
'l
2
Page 10 of 19

Design of RipRap Outlet Protection
Project: Nordfab
Proj. No: 210238.00
Client:
Nordfab/Fourth Elm
Date:
20-Jun-22
Revised:
21-Sep-22
Site Location (City/Town)
Culvert Id.
Total Drainage Area (acres)
Thomasville
Slope Drain
4.97
Step 4 - Determine the maximum stone diameter:
dmax = 1.5 x d50
Minimum TW
Max Stone Diameter, dmax (ft.) 0.75
Step 5 - Determine the apron thickness:
Apron thickness = 1.5 xdmax
Apron Thickness(ft.)
dm
—p
Davis • Martin • Powell
6415 Old Plank Road
High Point, NC 27265
p. 336.886.4821
Maximum TW
0
Minimum TW Maximum TW
1.125 0
Step 6 - Fit the riprap apron to the site by making it level for the minimum length, L,
from Figure 8.06a or Figure 8.06b. Extend the apron farther downstream and along
channel banks until stability is assured. Keep the apron as straight as possible and
align it with the flow of the receiving stream. Make any necessary alignment bends
near the pipe outlet so that the entrance into the receiving stream is straight.
Some locations may require lining of the entire channel section to assure stability.
It may be necessary to increase the size of riprap where protection of the channle side
slopes is necessary (Appendix 8.05). Where overfalls exist at pipe outlets or flows are
Page 11 of 19

Figure 8.06a: Design of outlet protection from a round pipe flowing full,
minimum tailwater condition (Tw<0.5 diameter)
20
10
0
3 0
Outlet W . Do + La
pipe
diameter (Do)
Tjilwater < 0.5Do
NV 70.
ok Pp 60
e50
m
3 5 10 20 50 100 200 500 101
Discharge (Olsec)
Curves may not be extrapolated.
Figure 8.06a Dosign of outlet protecwn protection from a round pipe flowing full, minimum tailwater condition (T. c 0.5 diameter)
it". IM 8.04

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Figure 8.06b: Design of outlet protection from a round pipe flowing full, m
tailwater condition (Tw>=0.5 diameter)
3Do
Oullet W = Do + 0.41-a
pipe i
diameter (Do) I La
i r .5Do
20
10
0
so 100
Discharge (Olsec)
Curves may not be extrapolated.
Figure 8.06b Design of outlet protection from a round pipe flowing full, maximum tailwatsr condid'on (Tw a 0.5 diameter).

iaximum
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J